This invention relates to a pressure reducer for compressed gases which, although its use is particularly advantageous in internal combustion engine fuel supply systems, can also be used in all cases in which a gas has to be taken from a high pressure to a lower pressure, such as ambient pressure.
The reducer in accordance with the invention is very compact, and so sensitive that a small vacuum at the outlet is sufficient to ensure that the reducer supplies a large amount of gas. In the description below, specific reference will be made to the case of a pressure reducer designed for installation in the gas supply system of an internal combustion engine, but the same concepts could obviously be applied in different situations, so the invention is not limited to the specific embodiment described here but extends to all applications in which the reducer could be used.
In pressure reducers of the type used in vehicle fuel supply systems, gas which is already at a stabilised pressure is fed through a nozzle closed by a valve which regulates the gas flow in accordance with engine demand. This valve usually consists of a closing member such as a disc or the like that closes the gas outlet nozzle to the engine, and is fitted on a lever which is subject to the action of regulating devices on the opposite side. These devices usually include a membrane to which is fitted a cap with a pin that acts on the said lever from the opposite side to the one on which the closing member is located.
The membrane is subject on one side to a reference pressure which may be atmospheric pressure, and on the other to the force of a calibrating spring and a pressure which is a function of or basically corresponds to the pressure detected close to the Venturi tube of the engine intake manifold.
The spring acts on the membrane to maintain it in the valve closing position when it is in the rest condition.
During acceleration, a sufficient vacuum is created on the side of the membrane which communicates with the manifold inlet to ensure that the reference pressure on the opposite side counteracts the force exerted by the spring, and pushes the membrane to act on the lever and open the gas outlet nozzle.
To obtain the force required to counteract the spring even when the vacuum on one side of the membrane is minimal, the membrane must have a fairly large surface.
These known reducers are therefore rather bulky and therefore difficult to fit into the engine compartments of modern vehicles; moreover, their sensitivity is considered insufficient to meet current requirements.
A first solution to the problem of the insufficient sensitivity of these reducers is offered by Italian patent no. 1,099,007 (U.S. Pat. No. 4,289,106) filed by the same applicant.
That document describes a reducer which comprises two membranes: one is fitted with a cap with mechanical devices that act on a valve opening lever to counteract a spring which tends to keep the lever in the closed position, while the other, which is highly flexible, separates an inlet chamber to which part of the gas is conveyed from a chamber at the reference pressure or atmospheric pressure. Part of the gas introduced into this inlet chamber by a nozzle exits through a passage leading to the engine intake manifold, while part returns into circulation through a cavity located between the flexible membrane and a fixed wall which has an opening communicating with the area into which the gas is introduced by the said nozzle.
When suction is increased, the vacuum created sucks the free membrane against the said opening, thus closing the passage through which the gas is recirculated.
All the gas is then conveyed to the engine, so the vacuum created in the chamber by the gas exiting from the nozzle at high speed acts on the first membrane, counteracting the force of the spring and causing it to move in such a way as to control, via the lever, opening of the valve which closes the high-pressure gas inlet.
Although this solution ensures a good level of sensitivity, it still presents various drawbacks and limitations.
The fact that the gas inlet closing valve is fitted to a lever introduces friction which has an adverse effect on the sensitivity of the device, with the result that the membranes used need to be large enough to be deformed sufficiently even by minimal pressure differences.
Moreover, in these known devices the efficiency of the device declines when demand for fuel from the engine increases, and vice versa. For the reasons set out above, the need is felt in the industry for means able to reduce the pressure of compressed gases which are small enough to be easily fitted into the engine compartments of present-day vehicles, but have a very level of high sensitivity, so that the outlet gas flow can instantly be adapted to meet demand for fuel from the engine.
This problem is now solved by the present invention, which relates to a pressure reducer for compressed gases in which pressure reduction takes place in two separate stages, and the pressure which acts on the membrane that controls opening and closing of the gas outlet valve is detected by a mobile element which moves in such a way that the pressure is always detected at the point where its value is lowest.